The present invention relates to electrolyte compositions and electrochemical cells for use in alkali metal polymer batteries, particularly lithium polymer batteries. Lithium polymer batteries typically include a lithium metal negative electrode (anode), or other suitable lithium-containing substance such as lithium metal alloys or lithium metal oxides, a metal oxide positive electrode (e.g., lithium vanadium oxide), and a solid polymer electrolyte. During operation, lithium is oxidized at the anode and lithium ions move into the electrolyte and to the cathode. When the battery is charged, lithium ions are reduced (plated) at the anode. This is accompanied by movement of lithium ions into the electrolyte from the cathode.
Solid electrolytes include ionically conducting polymers. The solid polymer electrolyte is typically poly(ethylene oxide) (PEO) based, complexed with a lithium salt. Such batteries possess high-energy storage capacity and rechargeability. PEO-based electrolytes are generally useful at temperatures above the melting point of the PEO-based salt complex. PEO itself has a melting point of 65xc2x0 C. but this may be lowered by copolymerization and salt inclusion. The need to use PEO-based electrolytes at higher temperatures is primarily due to their high degree of crystallinity and the fact that lithium ion conduction takes place only through the amorphous region. This temperature dependence of the conductivity of PEO-based polymer electrolytes results in them being primarily used above ambient temperature. In lithium polymer batteries the temperature is often maintained and controlled at about 40xc2x0 C. to about 80xc2x0 C.
However, at temperatures above 65xc2x0 C., uncrosslinked PEO undergoes flow and creep. This can result in the loss of mechanical strength, depriving the polymer electrolyte the ability to prevent cell shorting due to the formation of lithium dendrites. Also, PEO chains can migrate to the lithium anode surface and the free hydroxyl groups on the PEO can react with a lithium metal surface irreversibly. This can cause the interfacial resistance to increase and result in failures in battery cycling at 80xc2x0 C. Thus, what is needed is an electrolyte that has the advantages of PEO, but fewer deficiencies.
The present invention provides solid polymer electrolyte compositions. In one embodiment, the solid polymer electrolyte composition includes: a crosslinked solid ionically conductive polymer having urethane groups, urea groups, thiocarbamate groups, or combinations thereof; inorganic oxide particles; and a salt; with the proviso that at 20xc2x0 C. there is less than about 1 wt-% liquid present in the electrolyte composition; and wherein the solid polymer electrolyte composition has an ionic conductivity of at least about 1xc3x9710xe2x88x924 S/cm at about 60xc2x0 C. Preferably, and significantly, the inorganic oxide particles are substantially covalently bonded to either the polymer or other inorganic oxide particles (i.e., each other) through urethane groups, urea groups, thiocarbamate groups, or combinations thereof.
In another embodiment, the present invention provides a solid polymer electrolyte composition that includes: a crosslinked solid ionically conductive polymer having urethane groups, urea groups, thiocarbamate groups, or combinations thereof; nanoparticles, wherein at least 50% of the nanoparticles have a smallest dimension less than about 50 nm; and a salt; with the proviso that at 20xc2x0 C. there is less than about 1 wt-% liquid present in the electrolyte composition; and wherein the solid polymer electrolyte composition has an ionic conductivity of at least about 1xc3x9710xe2x88x924 S/cm at 60xc2x0 C.
In yet another embodiment, the present invention provides a solid polymer electrolyte composition that includes: a crosslinked solid ionically conductive polymer that includes a poly(alkylene oxide) polymer having urethane groups; at least about 0.5 wt-% hydroxyl-functional inorganic oxide particles; and a salt; with the proviso that at 20xc2x0 C. there is less than about 1 wt-% liquid present in the electrolyte composition; and wherein the solid polymer electrolyte composition has an ionic conductivity of at least about 1xc3x9710xe2x88x924 S/cm at about 60xc2x0 C.
In another embodiment, the present invention provides a solid polymer electrolyte composition that includes: a crosslinked solid ionically conductive polymer that includes a poly(alkylene oxide) polymer having urethane groups, wherein the solid ionically conductive polymer is prepared from a polyisocyanate, a poly(alkylene oxide) polymer having an equivalent weight of about 1,000 to about 100,000, and a poly(alkylene oxide) polymer having an equivalent weight of about 150,000 to about 500,000; at least about 3 wt-% hydroxy-functional inorganic oxide particles; and a lithium salt; with the proviso that at 20xc2x0 C. there is less than about 1 wt-% liquid present in the electrolyte composition; and wherein the solid polymer electrolyte composition has an ionic conductivity of at least about 1xc3x9710xe2x88x924 S/cm at about 60xc2x0 C.
In still another embodiment, the present invention provides a solid polymer electrolyte composition that includes: a crosslinked solid ionically conductive polymer prepared from a polymer of the formula A-(alkylene oxide)n-A, wherein A is xe2x80x94OH, xe2x80x94NH2, or xe2x80x94SH, and n is at least about 10, and a molar excess of a compound of the formula Zxe2x80x94Rxe2x80x94T, wherein T is an organic group having a vinyl group, R is a divalent organic group, and Z is a functional group capable of reacting with xe2x80x94OH, xe2x80x94NH2, or xe2x80x94SH; at least about 0.5 wt-% hydroxyl-functional inorganic oxide particles; and a lithium salt; with the proviso that at 20xc2x0 C. there is less than about 1 wt-% liquid present in the electrolyte composition; and wherein the solid polymer electrolyte composition has an ionic conductivity of at least about 1xc3x9710xe2x88x924 S/cm at about 60xc2x0 C.
The present invention also provides gel electrolyte compositions. In one embodiment, a gel electrolyte composition includes: a crosslinked solid ionically conductive polymer having urethane groups, urea groups, thiocarbamate groups, or combinations thereof; inorganic oxide particles; and a liquid electrolyte including a liquid at 20xc2x0 C. and a salt; with the proviso that the gel electrolyte composition is nonswellable; and wherein the gel electrolyte composition has an ionic conductivity of at least about 1xc3x9710xe2x88x924 S/cm at about 20xc2x0 C.
In another embodiment, a gel electrolyte composition includes: a crosslinked solid ionically conductive polymer having urethane groups, urea groups, thiocarbamate groups, or combinations thereof; nanoparticles, wherein at least 50% of the nanoparticles have a smallest dimension less than about 50 nm; and a liquid electrolyte including a liquid at 20xc2x0 C. and a salt; with the proviso that the gel electrolyte composition is nonswellable; and wherein the gel electrolyte composition has an ionic conductivity of at least about 1xc3x9710xe2x88x924 S/cm at about 20xc2x0 C.
In yet another embodiment, a gel electrolyte composition includes: a crosslinked solid ionically conductive polymer that includes a poly(alkylene oxide) polymer having urethane groups; at least about 0.5 wt-% hydroxyl-functional inorganic oxide particles; and a liquid electrolyte including a liquid at 20xc2x0 C. and a salt; with the proviso that the gel electrolyte composition is nonswellable; and wherein the gel electrolyte composition has an ionic conductivity of at least about 1xc3x9710xe2x88x924 S/cm at about 20xc2x0 C.
In another embodiment, a gel electrolyte composition includes: a crosslinked solid ionically conductive polymer that includes a poly(alkylene oxide) polymer having urethane groups, wherein the solid ionically conductive polymer is prepared from a poly(alkylene oxide) polymer having a weight average molecular weight of about 1,000 to about 20,000 and a polyisocyanate; hydroxyl-functional inorganic oxide particles; and a liquid electrolyte including a liquid at 20xc2x0 C. and a salt; with the proviso that the gel electrolyte composition is nonswellable; and wherein the gel electrolyte composition has an ionic conductivity of at least about 1xc3x9710xe2x88x924 S/cm at about 20xc2x0 C.
In still another embodiment, a gel electrolyte composition includes: a crosslinked solid lithium-ion conductive polymer that includes a poly(alkylene oxide) polymer having urethane groups, wherein the solid ionically conductive polymer is prepared from a poly(alkylene oxide) polymer having a weight average molecular weight of about 1,000 to about 20,000 and a polyisocyanate; at least about 0.5 wt-% alumina particles; and a liquid electrolyte including a liquid at 20xc2x0 C. and a salt; with the proviso that the gel electrolyte composition is nonswellable; and wherein the gel electrolyte composition has an ionic conductivity of at least about 1xc3x9710xe2x88x924 S/cm at about 20xc2x0 C.
Such electrolyte compositions can be used in half cells that include a cathode and a current collector or in electrochemical cells that include a first electrode and a second electrode. Such electrolytes are particularly useful in alkali polymer batteries.
The present invention also provides methods of making electrolytes. In one embodiment of a process for making a solid polymer electrolyte, the method includes: combining a poly(alkylene oxide) polyol, a salt, and inorganic oxide particles; adding a polyisocyanate and an optional catalyst; and thermally treating the mixture (e.g., extruding) to form a solid polymer. The mixture can optionally include a processing solvent that is removed during the thermal treating step.
In one embodiment of a process for making a gel electrolyte composition, the method includes: combining a poly(alkylene oxide) polyol, a salt, a liquid, and inorganic oxide particles; adding a polyisocyanate and an optional catalyst; and thermally treating the mixture (e.g., extruding) to form a gel; wherein a majority of the liquid electrolyte remains in the gel. The mixture can optionally include a processing solvent that is removed during the thermal treating step.
In yet another process for making an electrolyte composition, the method includes combining a polymer (which typically includes water) of the formula A-(alkylene oxide)n-A, wherein A is xe2x80x94OH, xe2x80x94NH2 or xe2x80x94SH, and n is at least about 10, with a molar excess of a compound of the formula Zxe2x80x94Rxe2x80x94T, wherein T is an organic group having a vinyl group, R is a divalent organic group, and Z is a functional group capable of reacting with xe2x80x94OH, xe2x80x94NH2, or xe2x80x94SH to form a polyunsaturated poly(alkylene oxide) having a molecular weight of at least about 100,000. The method typically includes crosslinking (e.g., with ultraviolet radiation) the polyunsaturated poly(alkylene oxide).